Locked accounts and inactive accounts are separate. A locked account can still be activated.

How do you unlock the account?

What works:

Reset the userPassword using an appropriate LDIF.

What doesn't work:

Everything else I've tried, including deleting accountUnlockTime,

passwordRetryCount, and RetryCountResetTime.

To reset the password to the same value that was used previously, assuming the Directory Server password policy allows it (i.e., pwd-max-history-count is disabled), include the full userPassword entry, including the password hash, in the LDIF.
e.g.,